JP-S62-253560-A discloses a vehicle brake hydraulic controller in which the target slip ratio at the time of vehicle braking while turning is made lower than that at the time of braking while running straight to suppress the side skidding of the vehicle and to improve steering performance thereof.
However, since only the target slip ratio at the time of braking while turning is made lower in the conventional technology, traceability along a running line cannot be satisfied sufficiently.
On the other hand, JP-H11-115721-A discloses a road surface friction coefficient estimating device which estimates a road surface friction coefficient from lateral acceleration in the case that the steering angle is larger than a given value and estimates a road surface friction coefficient from longitudinal acceleration in the case that the steering angle is smaller than the given value.
However, the road surface friction coefficient can be estimated accurately from lateral acceleration only when steering is performed in attempting to generate lateral acceleration larger than the maximum lateral acceleration that can be generated at the friction coefficient of the road surface on which a vehicle is running (at the time of steering exceeding the limit of road surface conditions), that is, only when the maximum lateral acceleration is generated in the vehicle. In contrast, in the conventional technology, whether lateral acceleration is used or not is simply determined depending on whether the steering angle is larger than the given value or not. Hence, for example, lateral acceleration may be used sometimes in a state in which the maximum lateral acceleration is not generated. In this case, a value smaller than the actual road surface friction coefficient may be estimated.